Large system analysis of the secrecy sum-rates with Regularized Channel Inversion precoding

In this paper, we study the performance of the Regularized Channel Inversion (RCI) precoder in a multi-user MIMO system with malicious users. We consider the general case when the number of users per transmit antenna β can take any value. We derive the optimal regularization parameter that maximizes the achievable secrecy sum-rate via large-system analysis, which we show to be accurate via simulations. We find that the secrecy requirements limit the number of users per transmit antenna that can be served with non-zero sum-rate. We show that for large signal-to-noise ratio, RCI can achieve secrecy without reducing the sum-rate if β <; 1. If β = 1, this is still possible at a cost of less than 4dB in terms of transmitted power. If β >; 1, then the secrecy requirements result in a poor sum-rate.